The present invention relates to a process for producing fibrous or foil-like moldings made of a plastified mixture which is composed, based on its weight, of from 60 to 10% by weight of a carrier component and from 40 to 90% by weight of a phase change material, where, based on the weight of the plastified mixture, the carrier component comprises from 5 to 20% by weight of a polymer or polymer blend from the group of LDPE (low-density polyethylene), HDPE (high-density polyethylene), PMMA (polymethyl methacrylate), polycarbonate, and mixtures thereof, from 5 to 20% by weight of a styrene block copolymer, and from 0 to 20% by weight of one or more additives, and the phase change material has been selected from the group consisting of natural and synthetic paraffins, polyethylene glycol (=polyethylene oxide), long-chain dialkyl ethers, long-chain alkyl alcohols, low-molecular-weight highly crystalline PE waxes, and mixtures thereof, and the plastified mixture is extruded at a temperature of from 130 to 220° C. through an extrusion die to give fibrous or foil-like moldings.
The invention further relates to a fibrous or foil-like molding which, based on its weight, is composed of from 60 to 10% by weight of a carrier component and from 40 to 90% by weight of a phase change material, where, based on the weight of the molding, the carrier component comprises from 5 to 20% by weight of a polymer or polymer blend from the group of LDPE, HDPE, PMMA, polycarbonate, and mixtures thereof, from 5 to 20% by weight of a styrene block copolymer, and from 0 to 20% by weight of one or more additives, and the phase change material has been selected from the group consisting of natural and synthetic paraffins, polyethylene glycol, and mixtures thereof.
At the phase transition temperature of the phase change material (hereinafter abbreviated to PCM), the heat storage enthalpy of the fibers or foils of the invention (hereinafter also termed PCM fibers and, respectively, foils) is up to 230 J/g. The fibers or foils are suitable for producing textile and sheet materials, to which they give advantageous thermal properties. The PCM fibers/foils provide compensation for temperature changes by absorbing or emitting heat, by virtue of their high heat storage enthalpy. Textile materials that can be used are especially textile clothing composites, wovens and knits with other synthetic or natural textile fibers, and also engineering textiles and engineering textile composites. The PCM fibers of the invention can also be processed to give chopped PCM fibers or PCM staple fibers, these likewise being used in textile applications (thermally insulated apparel, engineering textiles).
The prior art discloses blends made of phase change materials (PCM) and of polymeric thermoplastic carrier components, such as polyethylene and polypropylene, and moldings produced therefrom. Relevant patent specifications describe inter alia the production of fibers by means of conventional melt spinning processes. Blends made of one or more PCMs and of a polymeric carrier component are hereinafter termed PCM-polymer compounds.
PCMs used preferably comprise paraffins, or else long-chain dialkyl ethers, long-chain alkyl alcohols, or low-molecular-weight, highly crystalline PE waxes. A fundamental problem with the use of paraffin is that it is subject to severe heating during the plastification or melting process and, after discharge from an extrusion die with the attendant pressure drop, it vaporizes and forms bubbles. The formation of bubbles causes defects in the extruded molding. In the case of melt spinning of fibers, this leads to break-off or filament fracture. It is moreover known that moldings produced from PCM-polymer compounds, for example pellets, foils, sheets, etc. liberate liquefied PCM (preferably paraffin) when the phase transition temperature is exceeded. This process is also termed “sweating” in technical circles and is attributable to PCM residing close to the surface. PCMs such as paraffins have poor or zero miscibility with a wide variety of polymers. However, by using plastification and/or melting and mechanical shear it is possible to emulsify paraffin in a polymeric carrier component. Within this type of melt emulsion, the paraffin takes the form of droplet-like inclusions or droplet-like domains. The PCM droplets or paraffin droplets are also found in the moldings produced from the melt. If the surface of the molding has defects resulting from production or use, for example cracks or fractures, liquefied PCM can escape from droplets located immediately below the surface when the phase change temperature is exceeded, and can be emitted into the environment.
U.S. Pat. No. 5,885,475 describes the production of melt-spun polyolefin fibers which comprise, as phase change material, up to 60% by weight of unencapsulated crystalline hydrocarbons, such as paraffin. In order to bind the paraffin within the fiber and prevent sweating, a proportion by weight of from 7 to 16% by weight of silica particles is added to the melt or to the blend.
U.S. Pat. No. 4,737,537 and U.S. Pat. No. 4,908,166 relate to the production of chemically crosslinked PCM-polyethylene compounds, with the aim of achieving higher fill levels of PCM component in the polymer matrix. However, these chemically crosslinked PCM-polyethylene compounds are unsuitable for fiber production by means of conventional melt spinning processes, since the crosslinking begins to occur before the plastification/melting process has ended, and the associated viscosity increase inevitably reduces the spinning rate to a value which is not of any economic use.
DE 43 36 097 A1 (whose United States equivalents are U.S. Pat. Nos. 5,518,670 and 5,785,997) discloses a process for producing monofils made of filament-forming polymers via melt spinning. Filament-forming polymers mentioned are inter alia polyamides, polyesters, polyethylene, polypropylene, and polyacrylonitrile. Directly after discharge from the spinneret head, the monofils can be treated with blown air and cooled. They then pass through a liquid bath, the temperature of which is in the range from −10 to +150° C. This process is not very suitable for producing PCM-containing polymer fibers, because in the hot, thermoplastic state these have practically no tensile strength, and because of this they can immediately break off from the spinneret die under their own weight.
There are also processes known as bicomponent melt spinning processes, in which the extrusion die has two zones, so that a fiber is extruded with two filaments or regions spatially delineated from one another and made of different materials. US 2003/0035951 A1 and US 2007/0089276 A1 disclose processes of this type. Bicomponent fibers have by way of example a cross section of core-shell type or of multifilament (island-in-sea) type, where the core or the filaments is/are composed of a PCM and the sheath or the surrounding matrix is composed of a thermoplastic polymer. Bicomponent melt spinning processes have proven not to be very suitable for producing heat-storing, PCM-containing fibers. The extrusion heads required for this purpose have complex geometry and are susceptible to die blockage. This problem is intensified by the bubble formation described above and the attendant fiber break-offs, the residues from which cause caking at the spinneret dies. There is therefore a restriction on the proportion of PCM in the fiber in bicomponent fibers, to low values around 30% by weight. There is a corresponding restriction on the heat storage capacity achievable with bicomponent fibers.
One known method for avoiding the above problems is based on the use of PCM microcapsules in which there is a polymer envelope enclosing the PCM. The PCM microcapsules are incorporated into the carrier component in an upstream process step, preferably by means of an extruder. The plastified blend made of carrier component and of PCM microcapsules is extruded to give a strand and pelletized. The resultant pellets serve as starting material for the melt spinning process to give the fiber. Again, with this method there is a restriction on the quantitative proportion of the PCM in the pellets and therefore in the fiber, to values around 30% by weight. In order to incorporate more PCM into the fiber, it would be necessary to increase the amount, and therefore the density, of PCM microcapsules within the pellets to a value at which the intensive shear in the extruder causes increased destruction of the PCM microcapsules and liberation of PCM. The associated disadvantageous effects, such as bubble formation, have been described above.
US 2002/0105108 uses nylon-6-encapsulated PCM in polyethylene as carrier matrix, the proportion of PCM in the fiber being at most 30% by weight.
Other PCM-polymer compounds have been developed which are suitable for producing relatively substantial moldings. WO 2009/118344 A1 (=DE 10 2008 015 782) (and whose United States equivalent is United States Patent Publication No. 2011/193008) discloses a process for producing a thermoplastic material with heat storage enthalpy up to 135 J/g. The thermoplastic material includes a phase change material, in particular paraffin, and, as carrier component, a blend made of PMMA and of styrene block copolymers. The thermoplastic material is used to produce strand-extruded pellets. Production of fibers from the thermoplastic material is also provided, but without disclosure of any specific extrusion process for this purpose. The pellets of WO 2009/118344 A1 liberate practically no paraffin during extraction tests using cyclic temperature changes. From electron micrographs of cryofractured pellets it can be seen that the paraffin has been included in the form of droplet-like domains in the carrier component. The diameter of the paraffin domains is in the range from 10 to 100 μm.
Starting from the PCM-polymer compounds described in WO 2009/118344 A1 and from the processes for producing the same, the inventors have attempted to produce melt-spun fibers and extruded foils with from 40 to 75% by weight paraffin content and with fineness in the range from 5 to 70 tex and, respectively, with thickness of from 100 to 1000 μm. The problems that arose here were as follows:                numerous break-offs of the fiber/foil (in particular during orientation)        low breaking force of less than 3 cN/tex and, respectively, less than 30 N/mm2         a) high sweating losses.        
Said problems are believed to be attributable to the disadvantageous surface:volume ratio (˜1/radius and, respectively, ˜1/thickness) of fibers/foils. Fineness of from 5 to 70 tex corresponds to a fiber diameter of about 80 to 300 μm. According to the studies described in WO 2009/118344 A1 on strand-extruded pellets, the dimensions of the paraffin domains are in the range from 10 to 100 μm. Because the size of the paraffin domains is considerable in relation to the fiber diameter, and the fill levels are high, up to 75% by weight, it is highly probable that there are paraffin domains immediately adjacent to the fiber surface, which is large in relation to the fiber volume.
Small defects produced during spinning and orientation within the fiber surface can therefore lead to considerable paraffin losses and attendant structural weakening of the fiber, and to sweating. Similar problems arose in the production of extruded foils with thicknesses in the region below 1000 μm.